Silicon-based semiconductor devices are faced with the limitations of physical and nano-processing technology that cannot make them smaller anymore, due to continuously increased integration. Accordingly, development of a new electronic device is strongly required.
Spintronic devices that use both physical and electrical properties of electrons, i.e. electric charge and spin, are attracting much attention as next generation semiconductor devices, and a spin field effect transistor (hereinafter, a spin FET) that can change the resistance of devices according to the spin direction of actual electrons has recently been developed.
The spin FET has the same structure as the conventional silicon-based transistor (MOSFET) except that the source electrode and the drain electrode are made of a ferromagnetic material, and has advantages that it has a high operating speed and low power consumption because the resistance is changed by adjusting the spin direction.
The operating principle of the spin FET is that spin electrons polarized at the source electrode are injected into the transfer channel and the spin direction of the electrons moving in the transfer channel is controlled. The magnetization directions of the source and drain electrodes in response to an external magnetic field are fixed and the spin direction of the electrons injected into the transfer channel is controlled to be parallel or antiparallel using the electric field of the gate electrode. Here, if the spin direction of the electrons arriving at the drain electrode is parallel to the magnetization direction of the drain electrode, the resistance is low, and if it is antiparallel, the resistance is high.
Conventional spin FETs are currently operable only at extremely low temperatures below about 77K, due to their extremely low spin electron injection rates, short spin relaxation distances, high interface resistances between the source and drain electrodes and the channel, and a high signal to noise ratio.